1. Field of the Invention
The present invention relates to a seal structure of a tie rod mounting portion in a center take-off type power steering apparatus for a vehicle. More particularly to a seal structure of a tie rod mounting portion in a center take-off type power steering apparatus which improves a reliability for seal in a bolt passing portion of a dust boot passed through by a bolt in the tie rod mounting portion so as to be gripped.
2. Description of the Related Art
The conventional seal structure of the tie rod mounting portion in the center take-off type power steering apparatus is made as follows (refer to Japanese Patent Application No. 9-153292).
In FIG. 8, the structure is made such that respective inner ends of a pair of right and left tie rods 05 and 05 are respectively connected to a rack shaft 04 by a pair of right and left bolts 09 and 09 passing through a guide shoe 07 sliding within a notch groove 06 formed along a lengthwise direction of a gear box housing 03. It then moves laterally in correspondence to a lateral motion of the rack shaft 04 while being guided by the guide shoe 07.
A substantially center portion of a dust boot 011 is gripped between the guide shoe 07 and the respective inner ends of a pair of right and left tie rods 05 and 05 by being passed through by a pair of right and left bolts 09 and 09. Then, a metal fitting 013 is interposed between the dust boot 011 and the respective inner ends of a pair of right and left tie rods 05 and 05, and a collar 010 is fitted between the guide shoe 07 and the respective bolts 09 and between the dust boot 011 and the respective bolts 09 with overriding among the rack shaft 04, the guide shoe 07 and the guide boot 011.
One end portion (a lower end portion in FIG. 8) of the collar 010 protrudes from the dust boot 011 so as to be brought into contact with the metal fitting 013. Further, an annular protruding wall 025 is formed in the dust boot 011 so as to surround one end portion of the collar 010 and be brought into contact with the metal fitting 013.
Accordingly, as shown in FIG. 9, water going to enter from a direction of A is prevented by contact between the metal fitting 013 and the respective inner ends of a pair of right and left tie rods 05 and 05. The water going to enter from a direction of B is prevented by contact between the metal fitting 013 and one end portion of the collar 010 and contact between the metal fitting 013 and the annular protruding wall 025 of the dust boot 011. In the manner mentioned above, the water is prevented from entering into the dust boot 011 and further entering into the gear box 03.
However, since the conventional seal structure of the tie rod mounting portion in the center take-off type power steering apparatus is made as mentioned above, for example, there is generated a risk that a compressive reaction force F from the dust boot 011 acts on the seal structure as shown in FIG. 9. The force generates a stress in respective portions of the seal structure and breaks the seal structure, thereby reducing a waterproof performance when a force is transmitted to the dust boot 011 via the collar 010 in accordance with a lateral motion of the rack shaft 04. As a result, the dust boot 011 is extended and compressed to a rack end at a maximum stroke of the rack shaft 04. In this case, in FIG. 9, an arrow D indicates a moving direction of the rack shaft 04 and the tie rods 05 and 05.
In particular, the inner surface side of the dust boot 011 is pressed by the guide shoe 07 in the contact portion between the metal fitting 013 and the annular protruding wall 025 of the dust boot 011. Therefore, the compression reaction force F acts in a direction of contact with the metal fitting 013 in the outer surface side of the dust boot 011 and deforms the outer peripheral portion of the metal fitting 013 so as to bend outward toward the tie rods 05 and 05 side.
The metal fitting 013 is deformed in this manner, whereby a gap is generated in the contact portion between the metal fitting 013 and the annular protruding wall 025. There occurs a situation where water flowing towards the direction of B enters into the dust boot 011 via the gap and further into the gear box housing 03.
This situation is also generated in the same manner in the case that a tensile reaction force acts on the seal structure. Due to generation of this matter, there is a risk that a reliability with respect to the seal structure of the tie rod mounting portion in the center take-off type power steering apparatus is damaged.
In particular, since the compressive reaction force F and the tensile reaction force is further strengthened in the case that snow or the like are accumulated on a bellows portion of the dust boot 011 in winter season and the bellows can not move, the risk mentioned above is further increased.
The applicant of the present application has made an original idea of a seal structure of a tie rod mounting portion in a center take-off type power steering apparatus which can solve the problems mentioned above. It is provided in the conventional seal structure of the tie rod mounting portion in the center take-off type power steering apparatus, and can prevent the stress from being generated in the seal structure even when the force is transmitted to the dust boot via the collar. This happens in accordance with the lateral motion of the rack shaft and the dust boot is extended and compressed to the rack end at the maximum stroke of the rack shaft, thereby maintaining a waterproof performance and improving a reliability of the seal, and has filed a patent application (refer to Japanese Patent Application No. 11-1054).